Bags made of thermoplastic materials are usually not heat-sterilizable when empty since the inside surfaces of the bag, which have optimum sealing properties, are frequently in intimate contact with each other due to heat sterilization and even adhere to each other. With customary hot steam sterilization at a temperature of approximately 121.degree. C., such a clinging together of the inside surfaces of such bags is thus the rule such that only little liquid may be introduced into these bags, unless the liquid is added to the bag chamber under elevated pressure. However, even with such pressure treatment it is not possible to guarantee that tightly adhering points will be released.
To combat adhesion at relatively large areas of the surfaces, bag films have been mechanically pretreated in the prior art. Thus, for example, the surfaces have been roughened or raised points have been incorporated into the surfaces, for example, punctiform bumps, grooves, or ridges. The result is that the inside surfaces only cling to each other in a small surface area such that these areas are then released upon filling.
U.S. Pat. No. 3,211,144, for example, prevents the cohesion of the inside surfaces in that at least one of the inside surfaces is roughened by the use of a roller with an appropriately designed surface.
Etching or sandblasting are mentioned as other possibilities for roughening the surface such that there is no longer adhesion of the inside surfaces.
However, such treatment of the film surfaces is very time consuming and costly.
Consequently, medical bags are still primarily heat sterilized using the method whereby the bag is filled before sterilization with air or liquid such as water or already filled with the medical fluid to be used, and heat sterilization is then undertaken. Such a process is also disclosed in EP-A1-0 114 964. There, medical containers formed by sealing films made of a polymer mixture are described. Before sterilization, the containers are filled with air, water, or a medical fluid.